Retraction and extension mechanism for a vehicle rear vision mirror

ABSTRACT

This invention relates to a retraction and extension mechanism for extending or retracting a set of telescopic supports that connect a mirror head ( 10 ) to a mirror mounting bracket ( 11 ). It comprises a mirror mounting bracket ( 11 ) with a first tube ( 18 ) projecting from the mounting bracket ( 11 ). The mirror head ( 10 ) has a support ( 19 ) projecting from it that locates into and slides back and forth within the first tube ( 18 ). A roller ( 34 ) is mounting with respect to the support ( 19 ) and cable ( 29 ) is attached at one end with respect to the first tube ( 18 ) and a point between the roller ( 34 ) and the mirror head ( 10 ). It extends to and around the roller ( 34 ) and into the mirror head ( 10 ). The other end of the cable ( 29 ) extends into and is attached with respect to the first tube ( 18 ). A capstan ( 31 ) is located within the mirror head ( 10 ) and engages the cable ( 29 ). A motor ( 47 ) drives the capstan ( 31 ) in either direction to cause the mirror head ( 10 ) to extend or retract with respect to the mirror mounting bracket ( 11 ).

This invention relates to the extension or retraction of telescopicsupports that are used to secure the mirror head of a rear vision mirrorto a mounting bracket on a motor vehicle.

BACKGROUND OF THE INVENTION

Although one application is with a rear vision mirror assembly, itshould be realised that the invention should not be restricted to thisparticular application, as it will be suited to other applications.However, for ease of description, the invention will be described inrelation to this application.

It is desirable to be able to move the mirror head, which holds themirror, with respect to the mounting bracket on the motor vehicle intowards or away from the mounting bracket.

This enables the mirror head to be either positioned close to the sideof the motor vehicle, or to be extended away from the motor vehicle toprovide an increased field of view. A rear view may be obstructed by avehicle body, a load on the vehicle, or a trailer that is being towed.In many of these instances, extending the mirror head outwardly willprovide a increased field of view behind the vehicle.

Accordingly, it is an aim of the invention to provide a mechanism toextend or retract telescopic supports.

It is a further object of this invention to provide a means whereby amirror head can be both manually or automatically moved towards or awayfrom the mounting bracket of a motor vehicle mirror.

SUMMARY OF THE INVENTION

According to one aspect, the invention is a retraction and extensionmechanism for extending or retracting a set of telescopic supports thatconnect a mirror head to a mirror mounting bracket comprising:

a mirror mounting bracket,

a mirror head,

a first tube projecting from said mounting bracket,

a support projecting from said mirror head that locates into and slidesback and forth within said first tube,

a roller mounted with respect to said support,

a cable, attached at one end with respect to said first tube at a pointbetween said roller and said mirror head, and extending to and aroundsaid roller and into said mirror head, the other end of said cableextending into and attached with respect to said first tube,

a capstan within said mirror head engaging said cable, and

a motor to drive said capstan in either direction to cause said mirrorhead to extend or retract with respect to said mirror mounting bracket.

The support may also comprise a tube and more than one set of telescopicfirst and second tubes may be used to mount the mirror head to themirror bracket.

Preferably, a pair of first and second tubes are used, with one set offirst and second tubes being located above the other set. A first cableextends from a connector in the upper tube set into the mirror head,around the capstan and into the lower set of first and tubular arms,around a roller in the end of the second tube in the lower set and backto a connector. A second cable extends from the other side of the lowerconnector into the mirror head, around at least one idler pulley andthen into the upper set of first and second tubes. The end of thissecond cable is attached to the connector in the upper set via a rollerthat is mounted in the end of the second tube of the upper set. Movementof the first cable by the capstan will result in movement of the mirrorhead either towards or away from the mounting bracket. This will bedescribed in more detail below in respect of a preferred embodiment.

Further, the invention may comprise a drive means for a cord comprising:a pair of contra rotating capstans that are rotatably mounted to a motorhousing, said cable engaging with said capstans so that, with respect toeach direction of movement of said cable through said drive means, thecable moves around the axis of one capstan in a direction opposite tothat of the other capstan,

a pivot that allows said motor housing to rotate about an axis which isparallel to the axis of rotation of each of the capstans so that theextent of contact between the cable and the periphery of each capstancan be varied, and

torsion means acting with respect to said motor housing and pivot thatacts to rotate said motor housing and to increase the extent of contactof said cable with respect to the periphery of each said capstan.

Preferably, the pivot is located equally distant between the axis ofrotation of each capstan. This ensures that the extent of rotation ofthe axis of each capstan around the pivot is the same.

The torsion means may comprise either a torsion spring concentric withthe pivot, or a coil spring fixed at one end with respect to the mirrorhead and attached to the motor housing at the other. The torsion meansacts to rotate the motor housing in a direction which increases theextent of cable which is in contact with the periphery of each of thecapstans. The torsion means is required to maintain at least a minimumdegree of contact to ensure adequate drive connection between each ofthe capstans and the cable. If the extent of contact between the cableand the capstans becomes less than the minimum, then the cable will slipwith respect to each of the capstans.

In one aspect of the invention, this is quite useful. If movement of thecable is prevented for whatever reason, then continued rotation of thecapstans will tend to rotate the motor housing so that the extent ofengagement between the cable and each of the capstans is reduced. Thisrotation, against the torsion means, will continue until the capstansstart slipping with respect to the cable. At this point, the motorhousing will cease rotating while maintaining sufficient force to actagainst the torsion means, and to thereby prevent any overload orstalling of the capstans. It will also be useful if the mirror head ismoved manually. This will also cause rotation of the motor housing andresult in slipping of the cable.

Preferably, one of the capstans is driven by an electric motor viareduction gearing, and the other capstan is driven via engaging ringgears that are on each of the capstans. This results in the contrarotation of the capstans.

The cable used on both the means for moving the mirror head and thedrive means may comprise in a cord, belt or any other form of flexiblecord. In addition, multiple cables may be used to produce a series ofparallel cables that, together, act as a single cable.

As an alternative to contra rotating capstans, a single driven capstanmay be used. The capstan may be spring loaded, or arranged in some othermanner, so that it is pushed into the cable. The resultant angle of wrapmust be sufficient to enable drive force to be applied to the cable. Anyresistance to movement or any manual movement of the mirror head willresult in deflection of the spring and slippage of the cable over thecapstan.

A further alternative for the drive means may be a capstan incombination with a clutch. The clutch is designed to disengage uponmanual movement or any resistance to movement being encountered.

In a second aspect, the invention is a retraction and extensionmechanism for extending or retracting telescopic supports that connectsa mirror head to a mirror mounting bracket comprising:

at least one first tube attached at one end to, and projecting from,said mirror mounting bracket,

at least one support attached to and projecting from said mirror head,that locate into and slide back and forth within a said first tube,

at least one wheel secured with respect to said support, the peripheryof said wheel engaging against said first tube, and

drive means for rotating said wheel in either direction to move saidfirst tube and support with respect to each other to cause said mirrorhead to extend or retract with respect to said mirror mounting bracket.

Preferably, the support comprises a tube and a pair of first and secondtubes are used with one set of first and second tubes being locatedabove the other set. The wheel and associated drive means may be locatedin one of the sets, or alternatively a wheel with associated drive meansmay be located in each of the sets of first and second tubes.

Preferably, the mounting of the wheel within one of the tubes includes ameans of forcing the periphery of the wheel against one of the tubes.This may include a mounting which enables the wheel to move in adirection that is normal with respect to its axis of rotation and aspring means which pushes the wheel in the required direction.

Preferably, the wheel is mounted with respect to the tube which islocated internally of the other tube. An aperture may be provided withinthe internal tube to enable the periphery of the wheel to locate againstthe outer tube.

In addition to the use of one wheel, two or more wheels may be used toprovide the necessary drive force.

In addition to providing drive force, another function performed by thewheels will be to hold the mirror head in the required position while atthe same time allowing manual movement of the mirror head withoutoperation of the drive means. The friction force acting between theperiphery of the wheel and one of the tubes must be sufficient to enablethe wheel to move the mirror head. In addition, when the wheel isstationary, the applied force and resultant friction is high enough toprevent unwanted movement of the mirror head. The necessary force thatwill achieve these aims is not so large that it prevents manual movementof the mirror head. Manual movement will result in slippage of the wheelwith respect to one of the tubes. Accordingly, with this invention, itis possible to manually move the mirror head to an extended or retractedposition.

The wheel or wheels may be electrically driven, and the drive meanspreferably comprises an electric motor and drive pulley that is locatedwithin the mirror head and a cable which extends from the pulley intothe telescopic tubes and that engages the wheel so as to cause it torotate.

The cable within the telescopic tubes may either locate around theperiphery of the wheel or some other element of the wheel which causesit to rotate. Alternatively, a pair of spaced wheels may have the cablelocated around them with an idler pulley, positioned between the pair ofwheels, that pushes against the cable and in turn causes the cable topush against the pair of wheels. The pair of wheels may be slidablymounted with respect to their pivot to enable movement normal to theaxis of the pivot to thereby cause the periphery of the wheels to bearagainst the inside surface of one of the tubes.

In order to fully understand the invention, a preferred embodiment willnow be described, however it should be realised that the scope of thisinvention is not to be confined or restricted to the precise features ofthe embodiment.

DESCRIPTION OF THE DRAWINGS

The embodiment is illustrated in the accompanying illustrations inwhich:

FIG. 1 shows a schematic view of a mirror head, mounting bracket andlocation of drive means with associated cable according to a firstembodiment,

FIG. 2 shows a top view of a drive means illustrated in FIG. 1,

FIG. 3 shows a side view of a drive means illustrated in FIG. 1,

FIG. 4 shows a schematic view of a mirror head, mounting bracket anddrive means according to a second embodiment of this invention,

FIG. 5 shows a part schematic view of wheels and drive means inaccordance with a second embodiment,

FIG. 6 shows a schematic view of a mirror head, mounting bracket andlocation of drive means according to a third embodiment, and

FIG. 7 shows a part schematic view of wheels and drive means used in thethird embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a rear view mirror assembly according to a firstembodiment comprises a mirror head 10, a mounting bracket 11 and a upperand lower set of telescopic tubes 12 and 13 respectively. The mountingbracket 11 is attached to the side of the motor vehicle, and versions ofthe invention will be produced that are suited to both left and rightside applications.

The mirror head 10 carries the rear view mirror. The tilt of the mirroris controllable about a vertical and horizontal axis by electric motorsthat are commonly known and used in this industry. The mirror head 10comprises an assembly of a sub-frame 14 to which a moulded cover 15 issecured.

The telescopic tube sets 12 and 13 each comprise a first tube 18 that issecured at one end to the mounting bracket 11. The other end of eachfirst tube 18 locates through apertures within the moulded cover 15.

Supports, which comprise second tubes 19, are secured at one end to thesub-frame 14 and extend through the centre of each respective first tube18. The engagement of the first and second tubes 18 and 19 in thismanner enable the telescopic movement of the tube sets 12 and 13,thereby enabling the mirror head 10 to move toward or away from themounting bracket 11.

Friction pads 21 are generally drawn in FIG. 1, and comprise springloaded pads that exert pressure between the first and second tubes 18and 19 to prevent unwanted vibration of the mirror head 10 with respectto the mounting bracket 11. The friction pads also prevent unwantedmovement of the telescopic tube sets 12 and 13.

FIG. 1 illustrates a series of cables (referred to in more detail below)and a drive means 25 which are used to cause movement of the mirror head10 with respect to the mounting bracket 11.

Firstly, connectors 27 are secured to each of the outer tubes 18. Eachof the connectors 27 project through elongate slots within the innertube 19 to allow the necessary movement of the inner tube 19 withrespect to the outer tube 18. A first cable 29 is attached to the upperconnector 27 and extends from the connector 27 into the moulded cover 15of the mirror head 10. The first cable 29 extends around an idler pulley30 and then engages contra rotating capstans 31 and 32 of the drivemeans 25. The first cable 29 extends around another idler pulley 33 thatis mounted on the sub-frame 14 and a roller 34 that is mounted to theend of the lower second tube 19. The first cable 29 is then connected tothe lower connector 27.

A second cable 35 is attached to the lower connector 27 and extends intomoulded cover 15 of the mirror head 10 and around idler pulleys 36 and37. The second cable 35 then extends around roller 38 located at the endof the upper inner tube 19 and is then attached to the upper connector27.

The motor housing 40 of the drive means 25 has a pivot 41 which connectsthe drive means 25 to the sub-frame 14. This enables rotation of themotor housing 40 about the pivot 41. A spring 42 is secured at one endto the sub-frame 14, and at the other end to the motor housing 40. Thespring 42 acts as a torsion means and tends to cause the motor housing40 to rotate in an anti-clockwise direction as shown in FIG. 1. Thistends to increase the extent of contact between the periphery of each ofthe contra rotating capstans 31 and 32 and the first cable 29. Inaddition, it acts to maintain the required tension within the first andsecond cables 29 and 35.

Operation of the drive means 25 will cause the mirror head 10 to eithermove away from or towards the mirror mounting bracket 11.

In order to make the mirror head 10 move towards the mounting bracket11, the drive means 25 is operated so that contra rotating capstan 31 isrotated in an anti-clockwise direction. This in turn reduces the lengthof the first cable 29 and shortens the distance between the idler pulley30 and the upper connector 27. As the upper connector 27 is fixed withrespect to the mounting bracket 11, which means the mirror head 10 willmove towards the mounting bracket 11.

As the length of the first cable 29 between the idler pulley 30 andconnector 27 is being shortened, the length of the first cable 29between idler pulley 33 and roller 34 is being lengthened. This enablesthe inner tube 19 carrying the roller 34 to move towards the mountingbracket 11.

The movement of the inner tube 19 carrying roller 38 towards themounting bracket 11 results in movement of the second cable 35. As theroller 38 moves away from the upper connector 27, a force resultsbetween pulley 36 and the lower connector 27. The change in length ofthe second cable 35 between the upper connector 27 and roller 38 resultsin a shortening of the second cable 35 between the pulley 36 and lowerconnector 27. This in turn acts in a similar manner to the shortening ofthe first cable 29 between the upper connector 27 and the pulley 30 andresults in the inner tube 19 and therefore mirror head 10 moving closerto the mounting bracket 11.

In order to move the mirror head in the opposite direction away from themounting bracket 11 the direction of the contra rotating capstans 31 and32 are reversed so that the contra rotating capstan 32 rotates in ananti-clockwise direction. This results in the length of the first cable29 between roller 34 and pulley 33 being reduced which causes the mirrorhead 10 to move away from the mounting bracket 11. Consistent with thedescription of the mirror head 11 moving inwardly, the length of thefirst cable 29 between the pulley 30 and the upper connector 27increases with a resultant corresponding change in the various lengthsof the second cable 35.

The drive means of the first embodiment is illustrated in FIGS. 2 and 3.The drive means 25 comprises an upper and lower casing 44 and 45 whichhold the contra rotating capstans 32 and 31 and electric motor 47 withits associated drive gears.

The contra rotating capstans 31 and 32 are moulded components thatincorporate both the capstans 31 and 32 together with drive gears 48 and49. Respective capstans 31 and 32 and drive gears 48 and 49 rotate abouta common axis and are journalled with respect to the upper and lowercasings 44 and 45 so that the drive gears 48 and 49 mesh. Accordingly,rotation of the first capstan 31 will cause the second capstan 32 torotate in the opposite direction.

The drive motor 47 drives a first worm drive 50 which drives a gear 51of a second worm drive 52. The second worm drive 52 drives the drivegear 49 of capstan 31.

As seen in FIG. 1, the first cable 29 loops around capstan 31 in onedirection and in the opposite direction around capstan 32. The drivemeans 25 is pivotally mounted to the sub-frame 14 via a pivot 41 whichcomprises a pivot post 53. A spring 42 is used to control the angle ofwrap of the first cable 29 around each of the capstans 31 and 32. Byensuring sufficient wrap of the first cable 29 around the capstans 31and 32, sufficient drive force can be imparted to the first cable 29 tocause movement of the mirror head 10.

If the mirror head 10 becomes jammed, either when it is moving inwardlyor outwardly, or if the mirror head 10 is moved manually either inwardlyor outwardly, the drive means 25 will tend to rotate about pivot 41 sothat the degree of wrap around the capstans 31 and 32 of the first cable29 reduces sufficiently to enable it to slip with respect to thecapstans 31 and 32.

If the mirror head becomes jammed as it is being driven in eitherdirection, the first cable 29 will become stationary, and the contrarotating capstans 31 and 32 will cause the drive means 25 to rotateabout its pivot 53. This will in turn act to reduce the angle of wrap ofthe first cable 29 around the capstans 31 and 32. This results from thespacing of pulley 30 on a first side of the drive means 25 and withpulley 33 positioned on the other side of the drive means 25. Once theangle of wrap reduces sufficiently, then the cable 29 will slip withrespect to the drive means 25.

If the mirror head 10 is being moved manually inwardly, the first cable29 will be attempting to lengthen itself between capstans 32 and 34.Because of the positioning of pulley 33 to the right of the pivot 53,sufficient force will be applied to rotate the drive means 25 in aclockwise direction about pivot 53. This in turn will reduce the angleof wrap around both capstans 31 and 32 and will enable slippage of thefirst cable 29.

Alternatively, if the mirror head 10 is being pulled outwardly, thelength of the first cable 29 between the upper connector 27 and capstan31 will be increasing. Initially, the force applied by this section ofthe first cable 29 will cause the drive means 25 to rotate in aclockwise direction as a result of the pulley 30 being located to theleft of the pivot 53. Again, this rotation will continue until the angleof wrap around both capstans 31 and 32 reduce sufficiently to enableslippage of the first cable 29.

Accordingly, the embodiments shown in FIG. 1 will enable the mirror head10 to be moved electrically by the drive means 25 while at the same timeproviding an over-ride mechanism that will enable manual movement oreffective disengagement of the drive means 25 should the mirror headbecome jammed.

A second embodiment of the invention is illustrated in FIGS. 4 and 5.FIG. 4 shows a schematic representation of the mirror head 10 and tofirst tubes 18. A single cable 55 is wrapped at least once around adrive pulley 56 and extends into the combined first and second tubes 18and 19 via pulleys 57. The cable 55 engages wheels 58, 59 and 61. Thereturned side of the cable 55 locates around pulleys 60.

The features of the invention shown in FIG. 4 are largely the same asthose shown in FIG. 1. The embodiment includes a subframe 14 withattached second tubes 19, outer tubes 18 which are also attached to amounting bracket 11 (not drawn). Pulleys 56, 57 and 60 are secured tothe sub-frame 14.

The drive pulley 56 is preferably driven by a small DC motor incombination with a worm drive and gear to provide sufficient drivetorque to pulley 56. In addition, the drive pulley 56 is slidablymounted with respect to the sub-frame 14, and a preloaded spring appliesa force between the subframe 14 and the drive pulley 56. This results ina pre-load or tension being applied to the cable 55. Pulleys 57 and 60are idler pulleys, and are used to route a cable 55 into and out of thesecond tubes 19.

The wheels 58, 59 and 61 are illustrated in more detail in FIG. 5. Eachof the wheels 58 and 59 are rotatably mounted with respect to the innertube 19 so that they are able to move normal to their axis of rotation.A pulley 61, which is also fixed with respect to the inner tube 19 actson the cable 55 between the wheels 58 and 59. The tension in the cable55 results in an outward force being applied by the cable to each of thewheels 58 and 59. The cable 55 preferably locates in a groove in theperiphery of each wheel 58, 59 and 61, and one length of the cable 55may pass between the inner and outer tubes 19 and 18.

An aperture 62 is provided in the inner tube 19 through which the wheels58 and 59 project so as to enable engagement against the inside surfaceof the outer tube 18. An aperture 65 in the inner tube 19 is providedthrough which the wheel 61 projects to enable contact with the tube 18.The tension in the cable 55 as a result of the positioning of pulley 61results in the wheels 58 and 59 bearing firmly against the insidesurface of the tube 18. The force applied by wheels 58 and 59 cause thetube 18 to bear against wheel 61. The resultant friction force willenable the wheels 58, 59 and 61 when rotated, to move the inner tube 19with respect to the outer tube 18, or when the mirror head 10 ismanually moved, to slip with respect to the inner surface of the outertube 18. Accordingly, if the mirror head 10 is moved manually, thewheels will not cause the cable 55 to back drive the drive pulley 56 andwill enable inward or outward movement of the mirror head 10 as a resultof the wheels 58, 59 and 61 slipping with respect to the outer tube 18.Movement of the cable 55 will rotate the wheel 61 in the oppositedirection to the wheels 58 and 59. This results in the required motiveforce being applied to the tube 18.

The force applied by the wheels 58, 59 and 61 to the outer tube 18 willalso act to hold the mirror head in position under normal operatingloads. Accordingly, vibration within acceptable limits will not resultin the mirror head 10 moving.

A third embodiment is illustrated in FIGS. 6 and 7. The arrangementshown in FIG. 6 is substantially the same as that shown in FIG. 4, theonly difference being the arrangement of wheels 58 and 59. Thisdifference is illustrated in FIG. 7.

In this embodiment, a third wheel 64 extends through a second aperture65 so that it bears against the inside surface of the outer tube 18. Apretension spring 66 applies a force between a mount 67 to which thewheels 58 and 59 are attached and a mount 68 to which the third wheel 64is attached. The spring 66 is selected so that the wheels 58, 59 and 64apply sufficient force to the inside surface of the outer tube 18. As inthe second embodiment, the wheels 58,59 and 64 are pivotally mountedwith respect to the inner tube 19, but are able to move normally withrespect to their axis of rotation so that force provided by the spring66 can be transferred to the inner surface of the outer tube 18.

In both the second and third embodiments, the cable 55 engages thewheels 58 and 59 so that they are rotated as the cable 55 is moved bythe drive pulleys 56. Upon operation of the electric motor that rotatesthe drive pulley 56, the wheels 58 and 59 rotate in the same directionand either move the inner tube 19 inwardly or outwardly with respect tothe outer tube 18.

As will be seen from the above descriptions, the three embodimentsprovide a simple and effective means of automatically moving telescopictubes with respect to one another. The invention will have particularapplication in relation to rear view mirrors, however the invention willbe equally suited to other applications involving the movement oftelescopic tubes.

The claims defining the invention are as follows:
 1. A retraction andextension mechanism for extending or retracting a set of telescopicsupports that connect a mirror head to a mirror mounting bracketcomprising: a mirror mounting bracket, a mirror head, a first tubeprojecting from said mounting bracket, a support projecting from saidmirror head that locates into and slides back and forth within saidfirst tube, a roller mounted with respect to said support, a cable,attached at one end with respect to said first tube at a point betweensaid roller and said mirror head, and extending to and around saidroller and into said mirror head, the other end of said cable extendinginto and attached with respect to said first tube, a capstan within saidmirror head engaging said cable, and a motor to drive said capstan ineither direction to cause said mirror head to extend or retract withrespect to said mirror mounting bracket.
 2. A retraction and extensionmechanism according to claim 1 wherein said support comprises a secondtube.
 3. A retraction and extension mechanism according to claim 1wherein the end of said first tube locates within said mirror head inits fully extended position.
 4. A retraction and extension mechanismaccording to claim 1 further comprising a connector attached to saidfirst tube, each end of said cable attached to said connector.
 5. Aretraction and extension mechanism according to claim 1 furthercomprising a motor housing within which said motor locates, said motorhousing secured within said mirror head.
 6. A retraction and extensionmechanism according to claim 5 further comprising a pair of capstansthat counter rotate with said cable wrapping around a first said capstanin one direction and the other said capstan in an opposite direction tothe first said capstan.
 7. A retraction and extension mechanismaccording to claim 6 wherein said cable engages only part of theperiphery of said first capstan and engages only part of the peripheryof said other capstan.
 8. A retraction and extension mechanism accordingto claim 7 wherein said motor housing is pivotally attached to saidmirror head and further comprising a spring acting between said mirrorhead and said motor housing that acts to tension said cable and maintainthe required degree of engagement of said cable around said capstans toprevent slippage of said cable with respect to said capstans.
 9. Aretraction and extension mechanism according to claim 8 wherein saidmotor housing is caused to rotate against said spring should themovement of said mirror head be impeded.
 10. A retraction and extensionmechanism for extending or retracting telescopic supports that connect amirror head to a mirror mounting bracket comprising: a pair of spacedparallel first tubes, each attached at one end to, and projecting from,said mirror mounting bracket, a pair of spaced parallel supports, eachattached to and projecting from said mirror head, that locate into andslide back and forth within said first tube, a roller mounted withrespect to one of said supports, a cable attached at one end withrespect to said first tube within which said roller locates at a pointbetween said roller and said mirror head, that extends to and aroundsaid roller and into said mirror head, the other end of said cableextending into and attached with respect to the other said first tube, acapstan within said mirror head engaging said cable, and a motor todrive said capstan in either direction to cause said mirror head toextend or retract with respect to said mirror mounting bracket.
 11. Aretraction and extension mechanism according to claim 10 wherein saidsupport comprises a second tube.
 12. A retraction and extensionmechanism according to claim 10 wherein the end of said first tubelocates within said mirror head in its fully extended position.
 13. Aretraction and extension mechanism according to claim 10 furthercomprising a connector attached to said first tube, each end of saidcable attached to said connector.
 14. A retraction and extensionmechanism according to claim 10 further comprising a motor housingwithin which said motor locates, said motor housing secured within saidmirror head.
 15. A retraction and extension mechanism according to claim14 further comprising a pair of capstans that counter rotate with saidcable wrapping around a first said capstan in one direction and theother said capstan in an opposite direction to the first said capstan.16. A retraction and extension mechanism according to claim 15 whereinsaid cable engages only part of the periphery of said first capstan andengages only part of the periphery of said other capstan.
 17. Aretraction and extension mechanism according to claim 16 wherein saidmotor housing is pivotally attached to said mirror head and furthercomprising a spring acting between said mirror head and said motorhousing that acts to tension said cable and maintain the required degreeof engagement of said cable around said capstans to prevent slippage ofsaid cable with respect to said capstans.
 18. A retraction and extensionmechanism according to claim 17 wherein said motor housing is caused torotate against said spring should the movement of said mirror head beimpeded.
 19. A retraction and extension mechanism for extending orretracting telescopic supports that connect a mirror head to a mirrormounting bracket comprising: a pair of spaced parallel first tubes, eachattached at one end to, and projecting from, said mirror mountingbracket, a pair of spaced parallel supports, each attached to andprojecting from said mirror head, that locate into and slide back andforth within said first tubes, a roller mounted with respect to each ofsaid supports, a first cable attached at one end with respect to one ofsaid first tubes at a point between said roller and said mirror head,that extends into said mirror head, the other end of said first cableextending into the other said first tube, around said roller in theother said first tube and fixed to the other said first tube at a pointbetween said roller and said mirror head, a second cable attached at oneend to said one of said first tubes, at a point between said roller andsaid mirror head, and extending to and around said roller and into saidmirror head, the other end of said second cable extending into andattached with respect to said other said first tube, a capstan withinsaid mirror head engaging said first cable, and a motor to drive saidcapstan in either direction to cause said mirror head to extend orretract with respect to said mirror mounting bracket.
 20. A retractionand extension mechanism according to claim 19 further comprising idlerpulleys within said mirror head engaged by said second cable.
 21. Aretraction and extension mechanism according to claim 20 furthercomprising roller pulleys within said mirror head engaged by said firstcable.
 22. A retraction and extension mechanism according to claim 19wherein said support comprises a second tube.
 23. A retraction andextension mechanism according to claim 19 wherein the end of said firsttube locates within said mirror head in its fully extended position. 24.A retraction and extension mechanism according to claim 19 furthercomprising a connector attached to each said first tube, respective endsof said first and second cables attached to a respective connector. 25.A retraction and extension mechanism according to claim 19 furthercomprising a motor housing within which said motor locates, said motorhousing secured within said mirror head.
 26. A retraction and extensionmechanism according to claim 25 further comprising a pair of capstansthat counter rotate with said first cable wrapping around a first saidcapstan in one direction and the other said capstan in an oppositedirection to the first said capstan.
 27. A retraction and extensionmechanism according to claim 26 wherein said first cable engages onlypart of the periphery of said first capstan and engages only part of theperiphery of said other capstan.
 28. A retraction and extensionmechanism according to claim 27 wherein said motor housing is pivotallyattached to said mirror head and further comprising a spring actingbetween said mirror head and said motor housing that acts to tensionsaid first cable and maintain the required degree of engagement of saidfirst cable around said capstans to prevent slippage of said cable withrespect to said capstans.
 29. A retraction and extension mechanismaccording to claim 28 wherein said motor housing is caused to rotateagainst said spring should the movement of said mirror head be impeded.30. A motor vehicle mirror on a vehicle with a mirror head that isextendable or retractable with respect to said vehicle comprising: amirror mounting bracket, a mirror head, a first tube projecting fromsaid mounting bracket, a support projecting from said mirror head thatlocates into and slides back and forth within said first tube, a rollermounted with respect to said support, a cable, attached at one end withrespect to said first tube at a point between said roller and saidmirror head, and extending to and around said roller and into saidmirror head, the other end of said cable extending into and attachedwith respect to said first tube, a capstan within said mirror headengaging said cable, and a motor to drive said capstan in eitherdirection to cause said mirror head to extend or retract with respect tosaid mirror mounting bracket.
 31. A motor vehicle mirror on a vehiclewith a mirror head that is extendable or retractable with respect tosaid vehicle comprising: a pair of spaced parallel first tubes, eachattached at one end to, and projecting from, said mirror mountingbracket, a pair of spaced parallel supports, each attached to andprojecting from said mirror head, that locate into and slide back andforth within said first tubes, a roller mounted with respect to one ofsaid supports, a cable attached at one end with respect to said firsttube within which said roller locates at a point between said roller andsaid mirror head, that extends to and around said roller and into saidmirror head, the other end of said cable extending into and attachedwith respect to the other said first tube, a capstan within said mirrorhead engaging said cable, and a motor to drive said capstan in eitherdirection to cause said mirror head to extend or retract with respect tosaid mirror mounting bracket.
 32. A motor vehicle mirror on a vehiclewith a mirror head that is extendable or retractable with respect tosaid vehicle comprising: a pair of spaced parallel first tubes, eachattached at one end to, and projecting from, said mirror mountingbracket, a pair of spaced parallel supports, each attached to andprojecting from said mirror head, that locate into and slide back andforth within said first tubes, a roller mounted with respect to each ofsaid supports, a first cable attached at one end with respect to one ofsaid first tubes at a point between said roller and said mirror head,that extends into said mirror head, the other end of said first cableextending into the other said first tube, around said roller in theother said first tube and fixed to the other said first tube at a pointbetween said roller and said mirror head, a second cable attached at oneend to said one of said first tubes, at a point between said roller andsaid mirror head, and extending to and around said roller and into saidmirror head, the other end of said second cable extending into andattached with respect to said other said first tube, a capstan withinsaid mirror head engaging said first cable, and a motor to drive saidcapstan in either direction to cause said mirror head to extend orretract with respect to said mirror mounting bracket.